Electrochemical and surface analytical studies of synergistic effect of phosphonate,Zn2+ and ascorbate in corrosion control of carbon steel

Synergistic inhibition of corrosion of carbon steel in low chloride environment using ascorbate as a synergist along with 2‐phosphonobutane‐1,2,4‐tricarboxylic acid (PBTC) and Zn²⁺ is presented. The synergistic effect of ascorbate has been established from the present studies. In the presence of ascorbate, lower concentrations of PBTC and Zn²⁺ are sufficient in order to obtain good inhibition, thus making this formulation more environmentally friendly. Potentiodynamic polarisation studies inferred that this mixture functions as a mixed inhibitor, predominantly cathodic. Impedance studies revealed that an immersion period of 24 h is necessary for the formation of the protective film, with a very high charge transfer resistance. The film is stable even at 60 °C in the presence of the inhibitor in the corrosive environment. The surface analysis by X‐ray photoelectron spectroscopy (XPS) showed the presence of iron, oxygen, phosphorus, carbon and zinc in the protective film. The XPS spectra inferred the presence of oxides/hydroxides of iron(III), Zn(OH)₂ and [Zn(II)–PBTC–ascorbate] complex in the surface film. This inference was further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. A plausible mechanism of corrosion inhibition has been proposed.     

Synergistic corrosion inhibition by the sodium dodecylsulphate-Zn system

The inhibition efficiency (IE) of sodium dodecylsulphate (SDS) in controlling corrosion of carbon steel immersed in the environment containing 60 ppm of Cl⁻, in the absence and presence of Zn²⁺ has been evaluated by weight-loss method. It is observed that SDS and Zn²⁺ individually are not good inhibitors. But their combination shows excellent IE. For example, 100 ppm of SDS has only 10% inhibition efficiency whereas 75 ppm of Zn²⁺ has 45% IE. Interestingly their combination shows 93% IE. This suggests that a synergistic effect exits between Zn²⁺ and SDS. The influence of pH on the IE of the SDS-Zn²⁺ system has been evaluated. The protective film has been analysed by Fourier transform infrared (FTIR) and fluorescence spectra. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from weight-loss method, and FTIR and fluorescence spectra. It is found that in the absence of Zn²⁺, the protective film consists of Fe²⁺-SDS complex formed on the anodic sites of the metal surface. In the presence of Zn²⁺, the protective film consists of Fe²⁺-SDS complex and Zn(OH)₂. The protective film is found to be UV-fluorescent.     

无磷海水缓蚀剂的开发

通过失重法测定腐蚀速率,并计算缓蚀率,确定了具有较好协同缓蚀效应的四元无磷海水缓蚀剂配方,并通过电化学极化、SEM、EDS等分析手段,对该无磷海水复合缓蚀剂的缓蚀机理进行了研究.结果表明:配方以40 mg/L钨酸盐+40 mg/L葡萄糖酸盐+4 mg/L Zn2++30 mg/L三乙醇胺为宜,该缓蚀剂在海水中对碳钢的缓...     

Corrosion behaviors of carbon steel in 55% LiBr solution containing PWVA inhibitor

The inhibition performance of PWVA inhibitor on carbon steel was studied in 55% LiBr + 0.07 mol/L LiOH solution. Results indicated that PWVA inhibitor decreased both anodic and cathodic polarization current density and widened the passive potential region of carbon steel in the test solution. It could be classified as mixed inhibitor. PWVA has a strong oxidizability. It could form an intact and compact film which consisted of Fe₂O₃ on carbon steel surface in the test solution. The passive film retarded Br^? which corroded the metal matrix in the test solution. When the concentration of PWVA was 300 mg/L, it showed an excellent inhibition effect. However, when the temperature was higher than 173 °C, the corrosion rate of carbon steel in 55% LiBr + 0.07 mol/L LiOH solution increased rapidly.     

Insights into the cut edge corrosion of 55% Al–Zn metal coating on steel from simultaneous electrochemical polarization and localised pH sensing experiments

Band microelectrode arrays were used to model the cut edge corrosion behaviour of 55% Al–Zn (Galvalume/Zincalume) and Zn coated steels in chloride and sulfate electrolytes. Simultaneous electrochemical polarization experiments revealed increased cathodic current on the steel during anodic dissolution of neighbouring Al–Zn alloy electrodes. The increased cathodic current on the steel was shown to be a result of pH buffering by Al³⁺, enhancing the rate of hydrogen evolution. A large negative shift of the corrosion potential of the Al–Zn alloy electrodes was observed during cathodic polarization on neighbouring steel electrodes and was attributed to alkaline pH generated from cathodic processes.     

Polyaspartic acid as a green corrosion inhibitor for carbon steel

The inhibitor effect of the environmentally friendly corrosion inhibitor polyaspartic acid (PASP) on the corrosion of carbon steel in 0.5 M H₂SO₄ was investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Polarization curve results clearly reveal the fact that PASP is a good anode‐type inhibitor. EIS results confirm its corrosion inhibition ability. The inhibition efficiency increases with increasing PASP concentration, and the maximum inhibition efficiency was 80.33% at 10 °C. SEM reveals that a protective film forms on the surface of the inhibited sample. The adsorption of this inhibitor is found to follow the Freundlich adsorption isotherm. A mechanism is proposed to explain the inhibitory action of the corrosion inhibitor.     

Synergistic corrosion inhibition study of Armco iron in sodium chloride by piperidin-1-yl-phosphonic acid-Zn system

Electrochemical techniques, weight loss method and surface analysis were used to study the synergistic inhibition offered by Zn²⁺ and piperidin-1-yl-phosphonic acid (PPA) to the corrosion of Armco iron in 3% chloride solution. It is observed that the combination between PPA and Zn²⁺ shows excellent inhibition efficiency. The potentiodynamic polarization curves reveal that 5 × 10⁻³ mol l⁻¹ of PPA has only 76.7% inhibition efficiency whereas the mixture containing 5 × 10⁻³ mol l⁻¹ PPA -20%Zn²⁺ has 90.2% inhibition efficiency. This suggests that a synergistic effect exists between Zn²⁺ and PPA. The Fourier transform infrared (FTIR) spectrum of the film formed on iron indicates phosphonates zinc salt formation. A suitable mechanism of corrosion inhibition is proposed based on the results obtained. The surface film analysis showed that in the absence of Zn²⁺, the protective film consists of Fe²⁺-PPA complex formed on the anodic sites of the metal surface, whereas in the presence of Zn²⁺, the protective film consists of Fe²⁺-PPA complex and Zn(OH)₂.     

Hydrogen absorption resulting from the simulated pitting corrosion of carbon-manganese steels

Hydrogen permeation measurements were performed on membranes of BS4360 Grade 50D C-Mn steel in the quenched and tempered condition. The rates of hydrogen absorption resulting from exposure to FeCl₂ solutions in a simulated corrosion pit were measured and found to be lower than those occurring in artificial sea water at applied potentials in the range commonly used for cathodic protection. A progressive decrease in the hydrogen permeation flux was recorded during simulated pitting and was attributed to the formation of a partially protective film of magnetite on the steel surface. At cathodic applied potentials iron plating was observed on the membranes. It is suggested that a similar process occurs in the cathodic protection of steel containing real corrosion pits and leads to a lowering of the Fe²⁺ ion concentration within the pits and a decrease in the aggressiveness of the local environment.     

Corrosion resistance of carbon steel in simulated concrete pore solution in presence of 1-dihydroxyethylamino-3-dipropylamino-2-propanol as corrosion inhibitor

The inhibition behaviour of 1-dihydroxyethylamino-3-dipropylamino-2-propanol (HPP) as an environment friendly corrosion inhibitor for reinforcing steel was investigated in simulated concrete pore solution contaminated by 0·1 mol L^?1 Cl^? by means of linear polarisation resistance, electrochemical impedance spectroscopy and cyclic voltammetry (CV). The surface morphology and corrosion products were also examined by scanning electron microscopy and X-ray diffraction (XRD). The results show that HPP can effectively inhibit the corrosion of reinforcing steel. The CV interpreted the corrosion inhibitor by restraining the reaction of cathodic reduction and anodic oxide. The XRD shows that the corrosion inhibitor reduces Cl^? adsorption on oxide film and reduces the production of corrosion products. In the conditions of this investigation, HPP behaves as an anodic corrosion inhibitor, protecting steel against corrosion in chloride contaminated environments.     

Evaluation of corrosion inhibitors for cooling water systems operating at high concentration cycles

The present work aimed at evaluating AISI 1020 carbon steel corrosion resistance of a 6:4:1:1 (MoO/HEDP/PO/Zn²⁺) inhibitor mixture present in a solution which simulates an industrial cooling water system operating at high concentration cycles (1050 ppm Cl⁻ and 450 ppm Ca²⁺). High concentration cycles are desirable, because system purge and treated water consumption are decreased. On the other hand, a high number of concentration cycles can increase the concentration of salts and dissolved impurities, causing corrosion, incrustations, and deposits inside the pipes, heat exchangers, and cooling towers. Thus, the chloride (Cl⁻) and calcium (Ca²⁺) ions aggressiveness was studied on the proposed inhibiting mixture, at the temperatures of 40 and 60 °C, through electrochemical techniques like open circuit potential measurements, anodic and cathodic polarization, and weight loss. The results showed that the inhibitor mixture conferred adequate protection to carbon steel in low concentrations, even in high aggressive media.     

Effects of Na3PW12O40 on the corrosion behavior of carbon steel in 55 %LiBr solution

Electrochemical technologies, chemical immersion tests and surface detection technologies were adopted to study the inhibition performance of Na₃PW₁₂O₄₀ inhibitor on carbon steel in 55 % LiBr + 0.07 mol/L LiOH solution, and the inhibition mechanism was discussed. Results indicated that Na₃PW₁₂O₄₀ inhibitor caused the decrease of both anodic and cathodic polarization current density and a widening of the passive potential region. It behaved as a mixed inhibitor. When the concentration of Na₃PW₁₂O₄₀ in 55 % LiBr + 0.07 mol/L LiOH solution was 300 mg/L, excellent inhibition performance on carbon steel was obtained. When the solution temperature were 145°C, 160°C, 180°C and 200°C, respectively, the corrosion rates of carbon steel were 13.07 μm/y, 17.74 μm/y, 24.55 μm/y and 73.52 μm/y accordingly. Na₃PW₁₂O₄₀ inhibitor exhibited an excellent inhibition performance at high temperature. Na₃PW₁₂O₄₀ is a strong oxidant. Fe was oxidized to Fe₂O₃ and itself was deoxidized to heteropoly blue. By this mechanism, an integrate compact passive film mainly comprising Fe₂O₃ may be formed on the carbon steel surface, and the corrosion of carbon steel in 55 % LiBr solution may be retarded by this passive film.     

Characterization of corrosion of X70 pipeline steel in thin electrolyte layer under disbonded coating by scanning Kelvin probe

Scanning Kelvin probe technique was used to characterize the electrochemical corrosion behavior of X70 steel in a thin layer of near-neutral pH and high pH solutions, respectively. Results demonstrate that passivity can be developed on steel in the near-neutral pH solution layer as thin as 60 μm, which is attributed to the fact that Fe²⁺ concentration in aqueous phase could reach saturation in the thin solution layer. The solubility of FeCO₃ is reached to drop out of solution as a precipitate. With the increase of solution layer thickness, it becomes more difficult for Fe²⁺ concentration to reach saturation. Consequently, the passivity cannot be maintained, and the steel shows an active dissolution state. Anodic dissolution rate of steel increases with the immersion time. The electrochemical polarization behavior of X70 steel in high pH solution is approximately independent of the solution layer thickness and immersion time. In thin solution layer, diffusion and reduction of oxygen dominate the cathodic process, as demonstrated by the presence of cathodic limiting diffusive current. In the bulk solution, the absence of limiting diffusive current density in cathodic polarization curve indicates that the main cathodic reaction is reduction of H₂CO₃ and , and the formed film is thus mainly FeCO₃.     

Influence of Zn on oxide films on Alloy 690 in borated and lithiated high temperature water

To clarify the corrosion control effect of Zn injection into hydrothermal environments, the oxide films on Alloy 690 in the deaerated borated and lithiated water have been investigated using potentiodynamic polarization curves, electrochemical impedance spectra at 300 °C and ex-situ X-ray photoelectron spectroscopy. With Zn injection in the solution, ZnCr₂O₄ and ZnFe₂O₄ were formed in the inner and outer layers of the oxide films on Alloy 690, respectively, through exchange reactions between Zn²⁺ and Fe²⁺/Ni²⁺. A simple model for oxide film structure change and the mechanism of corrosion inhibition by Zn injection is proposed and discussed.     

Synergism between Tartaric acid and Zinc ions under hydrodynamic conditions for corrosion inhibition of steel in cooling water solution-electrochemical impedance and morphological studies

A study of the St37 steel rotating disc electrode/cooling water interface was carried out using an environmentally friendly inhibitor mixture including Tartaric acid (TaA) and Zinc sulfate. Electrochemical Impedance Spectroscopy measurements were performed in the absence and presence of inhibitor in cooling water under static conditions and at different rotation speeds. TaA did not show good inhibition efficiency at quiescent conditions. However, its performance became significantly better in the presence of Zn²⁺ ions. The increase in electrode rotation speed also enhanced the inhibition efficiency of TaA and its mixture with Zn²⁺ ions. The synergism between TaA and Zn²⁺ ions and the solution hydrodynamics promoted the formation and adsorption of Tartrate-Zn²⁺ complexes on the metal surface, leading to a highly protective layer formed on metal surface as a barrier against diffusion of corrosive ions. Analysis by scanning electron microscopy and energy dispersive X-ray analysis was presented for both the corroded and protected metal surfaces. Based on results, a mechanism for corrosion inhibition and the synergism between two components was proposed.     

Effect of Fe-Zn alloy layer on the corrosion resistance of galvanized steel in chloride containing environments

In this study, the effect of Fe-Zn alloy layer that is formed during galvanizing process on the corrosion behavior of galvanized steel has been investigated. The galvanostatic dissolution of galvanized steel was carried out in 0.5 M NaCl solution to obtain the Fe-Zn alloy layer on the base steel. The alloy layer was characterized to be composed of FeZn₁₃, FeZn₇ and Fe₃Zn₁₀ intermetallic phases, which constitute the zeta, delta1 and gamma layers of galvanized steel, respectively. It was observed that the alloy layer has similar cathodic polarization behavior but different anodic polarization behavior compared to galvanized steel. The anodic current plateau of alloy layer was up to 100 times lower than that of galvanized coating. Corrosion test performed in wet-dry cyclic condition has shown that the alloy layer has lower corrosion rate as compared to galvanized steel. From the results of corrosion test of alloy layer and base steel, it was concluded that Zn²⁺ has positive effect on the protectiveness of the zinc corrosion products. The measurement of surface potential over the alloy/steel galvanic couple has confirmed the galvanic ability of alloy layer to protect both the alloy layer itself and the base iron during initial stage of atmospheric corrosion.     

钼酸盐复合缓蚀剂对海水中碳钢的缓蚀作用

采用失重法、极化曲线法和表面分析技术对钼酸盐复合缓蚀剂的缓蚀性能进行了研究,并通过试验确定了与钼酸盐有较好协同缓蚀效应的缓蚀剂配方。结果表明,单一钼酸盐对海水中碳钢的缓蚀率随着钼酸盐浓度的增加而增加,但钼酸盐浓度低于30 mg/L时存在加速碳钢腐蚀的情况。当钼酸盐为40 mg/L、有机膦酸盐(HEDP)为10 mg/L、Zn2 为4 mg/L、葡萄糖酸盐为50 mg/L时,该缓蚀剂对海水中碳钢的缓蚀率超过90%。钼酸盐复合缓蚀剂为阳极型缓蚀剂,海水中添加了缓蚀剂后碳钢试片表面形成了以氧化铁为主要成分,同时含有钼和磷的混合型沉淀膜。     

Inhibition mechanism of sodium laurate to underdeposit corrosion of carbon steels in NaCl solutions

Abstract

In a self-designed occluded corrosion cavity (OCC) simulated cell, the inhibition mechanism of sodium laurate (C₁₂H₂₃O₂Na) to the underdeposit corrosion of the N80 steel in a neutral 0·2 mol L^–1 NaCl solution was studied by electrochemical methods, including measurements of polarisation curves, coupling currents, polarisation resistances, electrochemical impedance spectra (EIS) and ion selectivity of the scale film. The results show that C₁₂H₂₃O₂^– could form a monomolecular adsorption film on the N80 steel surface in the studied solution, whose adsorption behaviour would follow Flory–Huggins isotherm model, and inhibit both anodic and cathodic processes. C₁₂H₂₃O₂^– displays good inhibition performance to the underdeposit corrosion of the N80 steel in the studied system, which could be mainly attributed to the inhibition to the electrode processes of the bulk cathode and occluded anode, the increase in the resistance of the corrosion deposit layer and the prevention to the autocatalysing acidification effect in OCC. The last two factors might be related to the conversion of the deposit layer from anion selectivity to cation selectivity and the formation of a hydrophobic layer on the wall of the micropores in the deposit layer by adsorption of C₁₂H₂₃O₂^–.     

The corrosion inhibitory property of N,N‐bis(2‐benzimidazolylmethyl)amine for Q235 steel

The main purpose of this paper is to systematically evaluate the anti‐corrosion property of N,N‐bis(2‐benzimidazolylmethyl)amine (IDB), which is a novel good thermal stabilized inhibitor in acidic medium. Results obtained from electrochemical tests and corrosion surface morphology analyses reveal that IDB performs excellently as corrosion inhibitor for Q235 steel in 1 mol/L hydrochloric acid corrosive solution. Potentiodynamic polarization measurements show that IDB inhibits both the anodic and cathodic processes of corrosion and exhibits as a mixed‐type inhibitor. Besides, the inhibiting efficiency (IE%) and consequently the degree of surface coverage (θ) increase with the inhibitor concentration rising. And when the concentration is 20 × 10^?5 mol/L, the corrosion inhibition effect is best to reach 96.39%. The adsorption of inhibitor on Q235 steel is found to obey the Langmuir adsorption isotherm, and the calculated Gibbs free energy demonstrates that IDB spontaneously adsorbs and forms a protective chemisorbed film on Q235 steel to restrain its corrosion. Hereby, IDB will become a promising corrosion inhibitor in further.     

The role of rusts in corrosion and corrosion protection of iron and steel

The processes of atmospheric corrosion of iron and steel and the properties of corrosion products (rusts) are modeled based on a quantitative evaluation of the chemical reactions pertaining to corrosion to elucidate the conditions with which corrosion-protective rust films form. Based on the model, it is suggested that in the initial stage of corrosion, in the rusts, the pH of the aquatic system is maintained at 9.31 owing to an equilibrium with iron(II) hydroxide and the rate of air-oxidation at this pH is very fast, and that dense, self-repairing rust films form, protecting the underlying iron and steel. However, after corrosion stops, the rust film deteriorates due to the dissolution and shrinkage by aging, and the deteriorated rust film separates the anode and cathode reaction products (Fe²⁺ and OH⁻ ions) to cause crevice corrosion. The air-oxidation of iron(II) in anode channels without the presence of OH⁻ ions results in strongly acidic solutions (pH 1.41), causing acid-corrosion. It is proposed that good catalysts (e.g. copper(II) and phosphate ions) accelerate the air-oxidation at low pH, delaying the crevice- and acid-corrosion stages. Further, it is argued that iron compounds with negative charges due to the non-stoichiometric proportions of the lattice oxide ions and metal ions (solid oxoanions of iron) exhibit stable cation-selective permeability even with a drop in pH. Rust films including such compounds would stop the passage of aggressive anions and act to protect iron and steel.     

Effect of Caand Mg on corrosion and scaling of galvanized steel pipe in simulated geothermal water

In this paper, the effects of scaling ions (Ca²⁺ and Mg²⁺) on corrosion and scaling processes of galvanized steel pipe in geothermal water are presented. Spherical corrosion products and needle-shaped scale coexisted on the pipe surface. The concentration of Zn²⁺ and OH⁻ affected the nuclei formation of scale. The corrosion products and scale were identified as Zn(OH)₂, ZnO, CaCO₃ and MgCO₃, respectively. When scale formed on the galvanized steel pipe, the corrosion rate slowed down and the pitting region became smaller.